Those layout guidelines on Brian's spreadsheet are a thing of beauty. Everything is lining up great (and quick!)
An externally hosted image should be here but it was not working when we last tested it.
Nice. Well at least the spreadsheet is calculating the panel sizes correctly (*phew*). And yes, the guidelines are very useful - makes it a lot easier to lay out the internal panels, compared to trying to measure offsets and angles to get them into the right locations. You just draw the guidelines, line up the internal panels along the guidelines, and that's it.
If I haven't said it before, MAKE SURE THAT YOU BRACE THE BOX PROPERLY. For a THAM-style fold, effective bracing MUST be placed in the first fold (S1,S2), and at also at the other side of the horn. I would recommend a full cross-braced, drilled out with a hole-saw to reduce its bulk while not reducing its effectiveness. While you can use left-over wood from the 18mm sheet for this, 12mm play will also work well, and even better if you use two such braces at the locations mentioned above.
The other sections can be braced effectively by short cross-braces.
Now we just need to see if the measured output is a close match for the sim 🙂.
No worries, I am bracing per martinsson's original THAM15 recommendations with some hole saw cuts here and there. Your spreadsheet guidelines makes it a snap to makes braces too!
I'm getting close to having the first box completed. Measurements will have to wait. It is -20 degrees F out tonight 🙂
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Measuring the impedance curve is usually the first thing on my list - at the very least you can use it to identify any problems in the build that should be corrected before any FR measurements.
One more thing - don't make the mistake of making the cutout hole for the driver the same size as specified in its documents. You're mounting the driver so it's facing into the hole, not so that it's magnet fits through the hole. It may be best to make the cutout about 4~6mm smaller in diameter. This will minimize the risk of introducing an air leak around where the driver is mounted to the cabinet.
One done. I can't say enough good things about your spreadsheet. If I wasn't messing around, I could have built two of these in one day.
I really like the THAM folding. It is easy to reach in and verify the last side panel seals to all of the internal panels.
I really like the THAM folding. It is easy to reach in and verify the last side panel seals to all of the internal panels.
An externally hosted image should be here but it was not working when we last tested it.
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Sound like a plan. I need to order some stuff but will get that done this week.
Brian if you have some pointers how to do that correctly I have no problem doing that.
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The easiest way would be to measure it using DATS, which is available from Parts Express. There is a cost associated with DATS, but I've found it one of the best additions to my loudspeaker DIY toolkit. There are also "free" ways of doing it, using freeware software and a rig that you put together yourself. You can also do it manually with a multimeter, a resistor and a spreadsheet to do the necessary calculations, and using your computer to provide the test tones at different frequencies, but that method can be a bit tedious.
I ordered DATS. It should be here tomorrow. I will try to test tomorrow night.
Do I need to break the driver in before I test anything. A friend recommended playing the driver at fs for any hour.
IMO it doesn't hurt to break it in (use a fairly large signal at the driver's Fs to get its excursion up to Xmax). Fifteen minutes should be enough, but no harm would be caused if you leave it to run longer. Driving it at Fs should keep the actual power dissipation low, but if the driver's magnet appears warm to the touch after the break-in period, allow it to cool down before performing the t/s test.
I've used my WT3/DATS to measure many drivers, but the majority of those were 12" and lower in diameter. The only time that the measurements appeared strange was when I measured the parameters for two B&C 18TBX100 drivers. Interestingly enough, once the drivers were placed in the horns they were going to be used in, the resulting impedance curve was a good match for my expectations.
For some background as to why I think measuring the impedance curve for a horn is an important part of the design-build-deploy process, have a look at the following links:
The Subwoofer DIY Page v1.1 - Projects : Using Impedance Graphs
OK, I set up and calibrated the DATS. Unfortunately I don't know exactly what I need to be looking at here.
I ran the impedence sweep and this is the output.
I ran the impedence sweep and this is the output.
An externally hosted image should be here but it was not working when we last tested it.
Sorry, I forgot to post that.
An externally hosted image should be here but it was not working when we last tested it.
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OK, I set up and calibrated the DATS. Unfortunately I don't know exactly what I need to be looking at here.
I ran the impedence sweep and this is the output.
Switch the vertical axis from a log to a linear scale.
You can also export the HornResp data and import it into DATS, which will make it easier to compare the predicted curve against the actual one. Any deviation between the two will stand out easier that way.
Hornresp in green, measured in blue
An externally hosted image should be here but it was not working when we last tested it.
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